Three hundred and seventeen cases of polyradiculoneuritis with Guillain-Barre syndrome (G.B. disease) (including 125 cases admitted to the pediatric clinic of the Okayama University Hospital) during the period from 1949 to 1955 were epidemiologically investigated. 1. The place of the most frequent occurrence was Minomicho, Numakuma-gun of Hiroshima Prefecture. Six cases were found there among 6406 residents (0.093%) 2. Regarding the age distribution, most of them were between 2 and 6 years of age. (The highest frequency of occurrence being at 4 years of age.) More patients were found in the farmer's or fisherman's families. Male patients were more than the female. 3. There was observed a tendency that the epidemy started at Okayama and moved gradually to the south-west. Epidemiological observation of the patients at Minomicho showed that this disease was obviously infectious. 4. More frequent occurrence was seen in July and August, i.e. the most moist and rainy season. 5. Constitutional factors may probably conceren the occurrence of this disease, 6. Incubation period is considered to be between 5 and 20 days.